This process with rotating forming rolls has been known and customary for many years and today represents one of the most widespread encapsulating processes for the manufacture of pharmaceutical, dietetic and technical capsules. Conventional rotary die processes are described for example in “Die Kapsel” [the capsule], Wissenschaftliche Verlagsgesellschaft MBH, Stuttgart, 1983.
A basic prerequisite for forming the capsules between the two forming rolls is to reach a sufficiently high temperature for fusing the two strips of material to form a seamless capsule. In the case of conventional gelatin capsules, the temperature of the wedge is about 43° C.+/−5° C. It is already known to arrange a heating device within the filling wedge to maintain the desired sealing temperature. The heating device may comprise heating cartridges fitted into the filling wedge or pipes for passing a liquid heating medium through, as described for example in EP-A-227 060.
These relatively high temperatures of the surface of the wedge sometimes have a harmful effect on the filling material. For instance, thermal decomposition may occur on account of the heat sensitivity of a wide variety of active substances. In the case of conventional material strips of gelatin, it is true that filling material temperatures of, for example, 25° C. to 35° C. can just about be maintained. When processing thermoplastic starch compositions, for example according to European Patent Application EP A 1 103 254, completely different temperature conditions are obtained, however. The material strips are produced by extrusion at temperatures above 100° C. and the melting point of the composition required for sealing is about 80° C. These much higher operating temperatures in the case of starch strips as opposed to gelatin strips are problematical for numerous filling materials. This applies to sensitive active substances but also to the preparation (pharmacological procedure), which is intended not to change with respect to viscosity and phases (emulsions, suspensions) under the effect of exposure to temperature.